ZeroEval Task Summary: math-l5

Example: 46

Question: The sum of a 15-term arithmetic series with first term 7 is $-210$. What is the common difference?

Correct Answer: 3

Example: 188

Question: In how many ways can one write the numbers 1, 2, 3, 4, 5, and 6 in a row so that given any number in the row, all of its divisors (not including itself) appear to its left?

Correct Answer: 25

Example: 261

Question: In the diagram, $K$, $O$ and $M$ are the centers of the three semi-circles. Also, $OC = 32$ and $CB = 36$.

[asy]
pair A, K, O, C, M, B, X, Y, Z, J, T;
O=(0,0);
C=(32,0);
M=(50,0);
B=(68,0);
A=(-68,0);
K=(A+C)/2;
X=(0,68);
Y=(-18,50);
Z=(50,18);
J=(7,43.3);
T=(59,15.6);
path nom, bigc, middlec, smallc;
nom=A--B--(100,100)--(-100,100)--cycle;
bigc=A..X..B--cycle;
middlec=A..Y..C--cycle;
smallc=C..Z..B--cycle;
fill(bigc, gray(.5));
fill(middlec, white);
fill(smallc, white);
draw(smallc);
draw(middlec);
draw(bigc);
draw(A--B);
label("A", A, S);
label("K", K, S);
label("O", O, S);
label("M", M, S);
label("C", C, S);
label("B", B, S);
label("S", J, SW);
label("E", T, SW);
label("$l$", (.9(J-T)+J), NW);
draw((.9(J-T)+J)--(.5(T-J)+T));
dot(K);
dot(O);
dot(M);
dot(J);
dot(T);
[/asy] Line $l$ is drawn to touch the smaller semi-circles at points $S$ and $E$ so that $KS$ and $ME$ are both perpendicular to $l$. Determine the area of quadrilateral $KSEM$.

Correct Answer: 2040

Example: 262

Question: A semi-circle of radius 8 cm, rocks back and forth along a line. The distance between the line on which the semi-circle sits and the line above is 12 cm. As it rocks without slipping, the semi-circle touches the line above at two points. (When the semi-circle hits the line above, it immediately rocks back in the other direction.) What is the distance between these two points, in millimetres, rounded off to the nearest whole number? [asy]

draw((-15, -8)--(15, -8));draw((-15, 4)--(15, 4));draw((-8, 0)--(8, 0){down}..{up}(-8, 0));

[/asy] (Note: After finding the exact value of the desired distance, you may find a calculator useful to round this value off to the nearest whole number.)

Correct Answer: 55

Example: 282

Question: Determine $w^2+x^2+y^2+z^2$ if
\[\begin{aligned} \frac{x^2}{2^2-1}+\frac{y^2}{2^2-3^2}+\frac{z^2}{2^2-5^2}+\frac{w^2}{2^2-7^2}&= 1 \\
\frac{x^2}{4^2-1}+\frac{y^2}{4^2-3^2}+\frac{z^2}{4^2-5^2}+\frac{w^2}{4^2-7^2} &= 1 \\
\frac{x^2}{6^2-1}+\frac{y^2}{6^2-3^2}+\frac{z^2}{6^2-5^2}+\frac{w^2}{6^2-7^2} &= 1 \\
\frac{x^2}{8^2-1}+\frac{y^2}{8^2-3^2}+\frac{z^2}{8^2-5^2}+\frac{w^2}{8^2-7^2} &= 1. \end{aligned}\]

Correct Answer: 36

Example: 288

Question: Let $x,$ $y,$ $z$ be positive real numbers. Find the minimum value of
\[\frac{(1 + 5z)(4z + 3x)(5x + 6y)(y + 18)}{xyz}.\]

Correct Answer: 5120

Example: 298

Question: The polynomial $f(x)=x^3-3x^2-4x+4$ has three real roots $r_1$, $r_2$, and $r_3$. Let $g(x)=x^3+ax^2+bx+c$ be the polynomial which has roots $s_1$, $s_2$, and $s_3$, where
\begin{align*}
s_1 &= r_1+r_2z+r_3z^2, \\
s_2 &= r_1z+r_2z^2+r_3, \\
s_3 &= r_1z^2+r_2+r_3z,
\end{align*}and $z=\frac{-1+i\sqrt3}2$. Find the real part of the sum of the coefficients of $g(x)$.

Correct Answer: -26

Example: 310

Question: Find the number of second-degree polynomials $f(x)$ with integer coefficients and integer zeros for which $f(0)=2010.$

Correct Answer: 163

Example: 328

Question: Compute the number of ordered pairs of complex numbers $(u, v)$ such that $uv = 10$ and such that the real and imaginary parts of $u$ and $v$ are integers.

Correct Answer: 48

Example: 331

Question: Let
\[x^8 + 98x^4 + 1 = p(x) q(x),\]where $p(x)$ and $q(x)$ are monic, non-constant polynomials with integer coefficients. Find $p(1) + q(1).$

Correct Answer: 20

Example: 333

Question: Given that a sequence satisfies $x_0=0$ and $|x_k|=|x_{k-1}+3|$ for all integers $k\ge1$, find the minimum possible value of $|x_1+x_2+\cdots+x_{2006}|$.

Correct Answer: 27

Example: 370

Question: Let $x_1,$ $x_2,$ $\dots,$ $x_{2016}$ be the roots of
\[x^{2016} + x^{2015} + \dots + x + 1 = 0.\]Find
\[\frac{1}{(1 - x_1)^2} + \frac{1}{(1 - x_2)^2} + \dots + \frac{1}{(1 - x_{2016})^2}.\]

Correct Answer: -338016

Example: 375

Question: For $x \ge 1,$ let $f$ be the function defined as follows:
\[f(x) = \left\{
\begin{array}{cl}
\lfloor x \rfloor \left| x - \lfloor x \rfloor - \dfrac{1}{2 \lfloor x \rfloor} \right| & \text{if $x < \lfloor x \rfloor + \dfrac{1}{\lfloor x \rfloor}$}, \\
f \left( x - \dfrac{1}{\lfloor x \rfloor} \right) & \text{otherwise}.
\end{array}
\right.\]Let $g(x) = 2^{x - 2007}.$ Compute the number of points in which the graphs of $f$ and $g$ intersect.

Correct Answer: 4022030

Example: 396

Question: Let $\mathbb{R}$ be the set of real numbers. Let $f : \mathbb{R} \to \mathbb{R}$ be a function such that for all real numbers $x$ and $y,$
\[f(x^2) + f(y^2) = f(x + y)^2 - 2xy.\]Let
\[S = \sum_{n = -2019}^{2019} f(n).\]Determine the number of possible values of $S.$

Correct Answer: 2039191